The present invention relates to clock controlled dual slope voltage to frequency converters. Various types of voltage to frequency converters are known and a useful summary of the various kinds is published in "Designing With Operational Amplifiers--Application Alternatives", 1977, Burr-Brown Research Corporation, Chapter 8.2 (pages 212-223). The highest precision form of converter as discussed in the above publication is the clock controlled converter which uses a precision clock signal to determine the duration of the constant current discharge pulse applied to the integrator circuit to provide dual slope operation. The problem with such clock controlled converters is that the frequency output signal of the converter is always a subharmonic of the clock frequency, although the average of the output signal frequency is the desired output frequency. As a result, although such converters can have high precision, they have an inherent delay resulting from the need to average the frequency of the output signal. An example of such a converter is shown in U.K. Patent Application Publication No. 2066626.
The present invention provides a converter which obtains the benefits of clock controlled operation whilst providing directly an output frequency which is not phase related to the clock frequency so that frequency averaging is not required.